Blog posts

Nature 439, 281 (2006)

The theoretical maximum tensile strain — that is, elongation — of a single-walled carbon nanotube is almost 20%, but in practice only 6% is achieved. Here we show that, at high temperatures, individual single-walled carbon nanotubes can undergo superplastic deformation, becoming nearly 280% longer and 15 times narrower before breaking. This superplastic deformation is the result of the nucleation and motion of kinks in the structure, and could prove useful in helping to strengthen and toughen ceramics and other nanocomposites at high temperatures.

The time-dependent plastic deformation (creep) behaviors of both the as-deposited and annealed plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiO_x) films were probed by nanoindentation load relaxation tests at room temperature. Our experiments found a strong size effect in the creep responses of the as-deposited PECVD SiO_x thin films, which was much reduced after rapid thermal annealing (RTA). Based on the experimental results, the deformation mechanism is depicted by the "shear transformation zone" (STZ) based amorphous plasticity theories. The physical origin of the STZ is elucidated and linked with the shear banding dynamics. It is postulated that the high strain gradient at shallow indentation depths may be responsible for the reduction in the stress exponent n=∂log(strain rate)/∂log(stress), characteristic of a more homogenous flow behavior.

Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percents. The films initially form in two different structures, one continuous and the other containing tri-branched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network.

In early days of Applied Mechanics News, I encountered a practical problem. How do we call ourselves? I began with a phrase "people in the international community of applied mechanics". The phrase is inclusive and descriptive, but is too long, too timid and too clumsy. It is like calling entropy "the logarithm of the number of quantum states". I have also heard the phrase "mechanics people", which I don't like either. It sounds too folksy, like calling a gynecologist a women's doctor.

More than fifty years ago, people realized that we can use fusion for energy, but the problem remains where and how to keep a plasma of 100 million degrees centigrade.

For TOKAMAK, one of the approaches to use the fusion power, now comes the news: "On 21 November, Ministers from the seven ITER Parties came together to sign the agreement to establish the international Organization that will implement ITER."

What might be the differences, if there is any, between mechanical signaling and chemical signaling in a living cell?